Presently available implantable stimulation devices, such as a cochlear implant device or a neural stimulator, typically have an implanted unit, an external ac coil, and an external control unit and power source. The external control unit and power source includes a suitable control processor and other circuitry that generates and sends the appropriate command and power signals to the implanted unit to enable it to carry out its intended function. The eternal control unit and power source is powered by a battery that supplies electrical power through the ac coil to the implanted unit via inductive coupling for providing power for any necessary signal processing and control circuitry and for electrically stimulating select nerves or muscles. Efficient power transmission through a patient's skin from the external unit to the implanted unit via inductive coupling requires constant close alignment between the two units.
Representative prior art cochlear implant systems are disclosed, e.g., in U.S. Pat. Nos. 4,532,930; 4,592,359; 4,947,844 and 5,776,172, all of which are incorporated herein by reference. Fully implantable cochlear implant systems are shown, e.g., in U.S. Pat. Nos. 6,272,382 and 6,308,101, also incorporated herein by reference.
Disadvantageously, each of the known prior art cochlear stimulation systems, except those that are fully implantable, requires the use of an external power source and speech processing system, coupled to the implanted stimulation device. For many patients, achieving and maintaining the required coupling between the external components and the implanted component can be troublesome, inconvenient, and unsightly. Thus, there exists a need and desire for a small, lightweight fully implantable device or system that does not require an external unit in order to be fully functional, that does not need constant external power, and that includes a long-lasting internal battery that may be recharged, when necessary, within a relatively short time period.
Moreover, even if a rechargeable battery were available for use within an implantable cochlear stimulation system, such rechargeable battery must not significantly alter the size of the existing implantable cochlear stimulator. This is because the curvature and thickness of the skull is such that there is only a limited amount of space wherein a surgeon may form a pocket wherein a cochlear stimulator may be implanted. This is particularly an acute problem for young children, where the thickness of the skull is relatively thin and the curvature of the skull is greater than for an adult. Thus, there is a need for a fully implantable cochlear implant system that is adaptable and lends itself for implantation within a range of head sizes and shapes.
Additionally, even where a rechargeable battery is employed within a fully implantable cochlear implant system, which fully implantable system includes an implantable speech processor and microphone, it may be necessary or desirable, from time to time, to replace the battery and/or to upgrade the speech processor hardware. Because implantation of the cochlear implant system, including insertion of the delicate electrode array into the cochlea of the patient, represents major surgery, which major surgery would hopefully only need to be performed once in a patient's lifetime, it is seen that there is also a need for a fully implantable cochlear implant system wherein the battery and/or speech processor may be replaced or upgraded from time to time through minimal invasive surgery, while leaving the implantable cochlear stimulator and delicate cochlear electrode array intact for use with the replaced battery and/or upgraded speech processor.
Further, should the internal battery or speech processor within the implant system malfunction, or should the user desire not to use the internal battery or speech processor for certain time periods, there exists a need to be able to power and operate at least the stimulator portion of the implant system from an external power source so that the implant system can continue to operate and provide its intended cochlea-stimulation function until such time as a new battery and/or upgraded speech processor can be safely implanted, or for as long as desired. This affords the patient the flexibility to select when additional implant surgery, if any, is to be performed, without having to shut down operation of the existing implant system. That is, the existing implant system may thus continue to operate with the assistance of an external power boost and/or external speech processor, for as long as necessary.